The present invention relates, in general, to semiconductor devices and, more particularly, to a quantum well semiconductor structure having high mobility intrinsic doping.
Semiconductor devices are formed on a substrate comprising semiconductor material. Intrinsic semiconductor material usually has very high resistivity or is semi-insulating. Conventionally, the resistivity of semiconductor material is lowered by doping portions of the semiconductor material with atoms that provide electrons or holes. For example boron is a P-type dopant in silicon, while phosphorous and arsenic are N-type dopants. This type of doping is called extrinsic doping.
One problem with extrinsic doping is that the dopant atoms increase scattering of charge carriers moving in the semiconductor material. Increased scattering is reflected in lower mobility in the semiconductor material. Moreover, lower mobility results in devices with slower switching and higher power consumption. This problem is addressed to some degree by modulation doping in heterostructure semiconductor devices. Modulation doping physically separates the dopant atoms from the charge carriers that they provide using quantum wells and barriers.
Native defects in the semiconductor crystal also cause scattering and mobility degradation. Modulation doping does not prevent scattering caused by native defects. Usually, manufacturers attempt to minimize the concentration of native defects to improve mobility. Unfortunately, native defects can have beneficial effects in a semiconductor structure, and minimizing their concentration also minimizes these beneficial effects.
What is needed is a semiconductor structure that beneficially uses properties of native defects while minimizing scattering and mobility degradation caused by the native defects.